1. Field of the Invention
The present invention relates to a heat insulating window film, a heat insulating material for a window, and a window. More specifically, the invention relates to a heat insulating window film, a heat insulating material for a window, and a window having excellent visible light transmittance and warming properties.
2. Description of the Related Art
In recent years, products with a lower environmental burden, which are so-called eco-friendly products have been required as one of energy saving measures for carbon dioxide reduction, and solar control window films for windows of vehicles or buildings have been required. A heat insulating window film is considered as such a product. The heat insulating window film is a film which delays transmission and reception of heat between an indoor side and an outdoor side by being attached to windows, and usage of heating is reduced by using this film, even in a case where a temperature on the outdoor side is lower than a temperature on the indoor side, and therefore, energy saving can be expected.
A degree of heat insulation is generally defined by using a coefficient of overall heat transmission and a small number means high heat insulating properties. According to JIS A 5759 (JIS stands for Japanese Industrial Standards), a coefficient of overall heat transmission can be acquired form reflection spectra of far infrared rays at a wavelength of 5 μm to 50 μm. When reflectivity of far infrared rays at a wavelength of 5 μm to 50 μm is increased, it is possible to decrease a coefficient of overall heat transmission, and thus, it is preferable to increase reflectivity of far infrared rays at a wavelength of 5 μm to 50 μm, in order to increase heat insulating properties.
Various configurations are known as methods of increasing reflectivity of infrared rays.
JP2006-264167A discloses that a layer reflecting infrared rays can be prepared by interposing a metal layer between two dielectric layers.
JP2006-264167A discloses a transparent heat shielding film formed of a surface protective layer, a primer layer, a heat shielding layer, and a base material and in which the heat shielding layer is formed by using a conductive polymer such as polyaniline.
JP2012-206430A discloses a laminated film in which a metal layer using silver as a main component and having a multi-layered structure including a far infrared reflection layer and a dielectric layer/carbon layer/hard coat layer are formed in this order on one surface of a base material formed of a synthesis resin, and an ultraviolet cutting layer is formed on the other surface of the base material.
Meanwhile, fibrous metal particles (for example, silver nanowires) or other fibrous conductive particles (carbon nanotubes and the like) are known as a material of a transparent electrode pattern in a touch panel field.
JP2012-238579A discloses a conductive member which includes a conductive layer containing conductive fibers using silver as a main component and having a short axis diameter equal to or smaller than 150 nm and three-dimensional cross-linking bond containing a bond represented by -M1-O-M1- (M1 represents an element selected from the group consisting of Si, Ti, Zr, and Al), on a base material and includes at least one interlayer between the base material and the conductive layer.
However, heat insulating properties of a layer using fibrous metal particles has not been concerned.